Phase-change materials (PCM) are capable of transforming between a crystalline phase to an amorphous phase and vice versa. These two solid phases exhibit differences in electrical properties, and semiconductor devices can advantageously exploit these differences. Given the ever-increasing reliance on radio frequency (RF) communication, there is particular need for RF switching devices to exploit phase-change materials. However, the capability of phase-change materials for phase transformation depends heavily on how they are exposed to thermal energy and how they are allowed to release thermal energy. For example, in order to transform into an amorphous state, phase-change materials may need to achieve temperatures of approximately seven hundred degrees Celsius (700° C.) or more, and may need to cool down within hundreds of nanoseconds.
A heating element repeatedly generating such high temperatures can experience a detrimental change in its resistivity over time. Undesirable change in the resistance of the heating element due to repeated OFF/ON cycling can cause a PCM RF switch to consume more power when switching between OFF and ON states. Resistivity change of the heating element can also result in the PCM RF switch taking longer when switching between OFF and ON states. Thus, resistivity change of the heating element is a figure of merit that can determine the marketability of the PCM RF switch and its suitability for a given application.
Accurately quantifying resistivity change of a heating element in a PCM RF switch can be problematic. Computer simulations cannot accurately predict the resistivity of the heating element over an entire lifetime. It might be necessary to perform more than one million OFF/ON cycles before the heating element exhibits any detectable resistivity change. Further, it might be necessary to detect resistivity change of the heating element in thousands of PCM RF switches in order to achieve statistically significant results regarding the degree of resistivity change for a given PCM RF switch design. Moreover, resistivity change due to repeated OFF/ON cycling is not easily distinguished from other changes due to the temperature coefficient of resistance (TCR) of the heating element.
Conventional techniques of testing RF switches, for example, by connecting external probes of an automated test equipment (ATE) to one RF switch at a time, have significant time delays that render generating large sets of test data impractical. When resorting to conventional testing in the context of PCM RF switches, time delays associated with generating the required temperatures to crystallize and amorphize the PCM in each individual RF switch additionally impede generating large sets of test data. Conventional means of testing can also introduce problems associated with the impedance of cables or wirebonds, and reduce the accuracy of test data.
Thus, there is need in the art to generate large sets of data for determining and characterizing resistivity change of heating elements in PCM RF switches accurately and rapidly.